Surfactants are well known materials which can be generally described as compounds having a hydrophobic moiety and a hydrophilic group per molecule. A wide variety of these materials are known and are classified as anionic, cationic, nonionic and amphoteric. They are well known to have numerous uses such as emulsifiers, detergents, dispersants and solubilizing agents in the field of cosmetics, textile treatment, industrial and personal cleaning preparations, corrosion inhibitors and the like.
Recently, a group of compounds having two hydrophobic moieties and two hydrophilic groups have been introduced. These have become known as "gemini surfactants" in the literature (Chemtech, March 1993, pp 30-33), and J. American Chemical Soc., 115, 10083-10090, (1993) and the references cited therein. Since their introduction, cationic and anionic "gemini surfactants" have been disclosed. Other surfactant compounds having two hydrophilic groups and two hydrophobic moieties have been disclosed but not referred to as gemini surfactants.
Sulfate, phosphate, and carboxylate surfactants are currently disclosed in the literature (See JAOCS 67, 459 (1990); JAOCS 68, 268 (1991); JAOCS 68, 539 (1991); and JAOCS 69, 626 (1992). Naturally derived, non-gemini surfactants are also known in the art. Most are nonionic and consist of a fatty acid chain that is linked to a sugar molecule usually by an ether ester or amide grouping. Being naturally derived from sources such as potatoes, wheat, beet sugar or corn starch, they are more environmentally friendly than conventional surfactants yet provide excellent foaming power, are mild to the skin and are useful in a wide variety of personal care, laundry and dishwashing products.
In nonionic surfactants, the surface-active portion of the molecule bears no apparent ionic charge. Usually polyethoxy chains, glycerides or polyhydroxy functional moieties, e.g. polyglucosides, constitute the hydrophile.
Single chain nonionics can also comprise sucrose esters which are prepared by reacting sucrose with edible fatty acids under controlled conditions in order to esterify the primary hydroxyl group of sucrose. The fatty acids such as stearic, palmitic and lauric can also be further reacted with other sugar moieties to produce di-, tri, and even higher esters.
Alkyl polyglucosides are prepared by one of two methods. In one, a direct process, glucose is reacted with a fatty alcohol in the presence of an acid catalyst. Excess alcohol is removed after neutralization. In the second method, a lower alcohol and a catalyst is utilized in a two step transacetylization process. When completed, the lower alcohol is replaced with a fatty alcohol.
Finally, glucosamide surfactants are prepared by reacting glucose with mono-methyl amine in the presence of hydrogen to form N-methyl glucamine. This is then reacted with a fatty ester to produce the glucosamide. These are particularly useful as co-surfactants. An anionic derivative of these is the sugar sulfosuccinates which are obtained by reacting ethoxylated .eta.-butyl glucosamide with maleic anhydride which is then sulfated with bisulfite. U.S. Pat. No. 5,622,938 to Wang discloses the use of sugar-based surfactants as carrier compounds for pharmaceutical actives.
Sugar-based gemini surfactants have also been previously described in the literature to a limited extent. U.S. Pat. No. 5,534,197 to Scheibel et. al. discloses and claims gemini polyhydroxy fatty acid compounds wherein the bridging group consists of a variety of alkyl, aryl, arylalkyl and aminoalkyl compounds having from about 2 to 200 atoms, and the hydrophobic heads are comprised of the same or different alcohol-containing moieties with two or more hydroxyl groups such as glycerol. The surfactants are asserted to be useful as active agents in laundry detergents, fabric cleaners, and personal care.
U.S. Pat. No. 5,403,922 to Garelli-Calvet et. al. discloses amphiphilic surfactants containing two sugar or sugar-derived head portions. The amphiphilic head portions are long chain aliphatic or branched aliphatic carbon chains. The chains are interrupted by various functional groups such as amines (--NH) and further comprise reducing glucosides comprised of a linear or cyclized carbon chain. The hydrophile is on the ends of the hydrophobe, constituting bola-type surfactants. Bola surfactants are relatively ineffective surface active compounds.
U.S. Pat. No. 5,512,699 to Conner et. al. discloses and claims poly-(polyhydroxy fatty acid amide) compounds that are asserted to be useful in laundry detergents, cleaning compositions, and personal care. Two identical long chain moieties containing hydroxyl groups are joined by a bridge consisting of polyethyleneimines, and polyethyleneamines with molecular weights below about 50,000 and preferably below 10,000. The hydrophobe is connected via carbonyl groups. U.S. Pat. No. 4,892,806 to Briggs et. al. discloses nonionic surfactants consisting of two R-groups consisting of substituted and unsubstituted alkyls, cycloalkyls, aryls or hydrogen that are joined by a carbon bridge to two hydrophilic groups represented by the formula --CH.sub.2 NHCO(CHOH).sub.x CH.sub.2 OH. The compounds are useful in emulsions for photographic light sensitive materials.
EPA 0 688 781 to Adams teaches and claims nonionic surfactants comprised of two polysaccharide sugar moieties that are linked to the central bridge of the molecule by one of their carbonyl groups. The central bridge is comprised of a polyalkyleneamine unit wherein at least one of the amine nitrogen atoms has a hydrophobic, substituted or unsubstituted hydrocarbon group linked thereto. The compounds are disclosed as being useful in aqueous hydrophilic colloid compositions such as light sensitive photographic materials.
PCT Application No. PCT/US95/00767 to Scheibel et. al. discloses and claims a class of gemini polyether fatty acid amides in which two polyethoxy, polypropoxy and/or mixed polyethoxypropoxy moieties of the general formula (CH.sub.2).sub.y O!H are joined by branched or linear alkyl or aryl moieties of from 2-200 carbon atoms. The surfactants may be combined with other nonionic and anionic surfactants and enzymes in soap and laundry detergent formulations.
PCT application No. PCT/US/00769 to Scheibel et. al. discloses and claims another class of polyhydroxy diamine compounds in which two "heads" consisting of reducing sugars such as glycerol, glucose, maltose, maltodextrin and the like are joined together by a unsubstituted, linear or branched alkyl, ether alkyl or amino alkyl consisting of from two to fifteen carbon atoms.
An article by Zhang et. al., J. Colloid. Interface Sci 177 419-426 (1996) discusses the effect of hydrophobic and hydrophilic chain lengths on the surface active properties of novel polysaccharide surfactants. The nonionic saccharide surfactants consist of an amide group that links a hydrophilic saccharide segment such as glucolactone, maltolactone, and dextrolactone to a hydrophobic alkyl segment such as hexylamine, octylamine and decylamine. It was shown that the size of the saccharide segment is important in determining the interfacial surface area of the molecule and hence it's surface activity.
Eastoe et. al., Langmuir. 12, 2701-2705 (1996) discloses nonionic amphiphile surfactants comprised of two .eta.-alkyl chains and two glucamide head groups. Surfactant purity, surfactant-water phase behavior, air-solution surface tension and small angle neutron-scattering characteristics are some of the surfactant characteristics disclosed. A second Eastoe et. al. article, Langmuir 10, 4429-4433 (1994) discusses the properties of nonionic surfactants comprised of two C.sub.6 hydrophobic chains and two glucamide head groups in the same fashion.
An article to Briggs et. al. J. Chem. Soc. 46, 379-380 (1995) briefly discusses the synthesis and properties of nonionic polyol surfactants derived from carbohydrate lactones. The surface properties of these nonionic gemini surfactants are rare and very few are reported in the literature.
Due to the need for new and more effective and efficient surfactants, as well as the need for mild surfactants which are biologically compatible in an ecologically sensitive environment, effort has been made to develop a new class of compounds which demonstrate improved surface-active properties that are further characterized as mild, and environmentally benign.
Single gemini surfactants that contain two hydrophilic heads and two lipophilic chains linked by a small bridge are able to demonstrate very special physical properties such as unusually low critical micelle concentrations (cmc) and pC.sub.20 values in aqueous media. It has been reported that ionic gemini surfactants can lower cmc values about 100 times more efficiently than single chain analogues and are about 1000 times more efficient at reducing the surface tension (pC.sub.20). Beside these outstanding physical properties, nonionic gemini surfactants can be very effective surface active agents, are biodegradable, and to a certain extent, are available from renewable resources such as natural fats and sugars. Therefore, sugar-containing surfactants have attracted considerable attention.
The new type of sugar gemini surfactant generally contains two aliphatic long chains as lipophilic groups and two oligosaccharides as hydrophilic heads. Because sugar molecules are very water soluble, they are superior as hydrophilic heads for gemini surfactants.
Like linear sugar-based surfactants, sugar gemini surfactants can use various forms of sugar as the hydrophilic groups such as glucose, fructose, maltose, lactose, galactose, mannose, xylose and so on. Other types of gemini surfactants generally contain a polyhydroxyl group as the hydrophilic head. Their general structure is shown below. ##STR2##
wherein R and R.sub.1 represent a C.sub.3 to C.sub.21 straight or branched chain hydrocarbyl moiety. See Eastoe, and Briggs, supra.
Sugar gemini surfactants have been prepared that contain two glucose hydrophilic groups and two hydrocarbon chains linked by an ethylene group. However, these bis-monosaccharide gemini surfactants are insoluble in water.